Viracept is a protease inhibitor supplied by Roche outside the United States and Canada. The United States, Canada, and Japan are not affected by the recall.

Roche received several reports that some batches of Viracept 250-mg tablets had a strange odor. A chemical analysis of the affected tablets showed they contained higher than normal levels of methane sulfonic acid ethylester.

Ethyl mesylate is a genotoxic substance, according to EMEA. “The level of risk to patients resulting from this contamination is difficult to measure, and is currently under further evaluation,” said EMEA in a press release.